Ear-buds or in-ear monitors can generate the sound waves required in the ear canal to create an auditory percept equivalent to sound experienced from free field loud speakers or from live music or speech. Auditory percepts, however, are only one aspect of the human experience of sound. The cutaneous sensory system is also capable of detecting low frequency sounds via the mechanical vibration of cutaneous sensory receptors. This is known as vibrotactile stimulation.
The skin has two different kinds of touch and two kinds of vibration receptors, also known as mechanoreceptors, relevant to the perception of vibrotactile stimulation: Meissner's corpuscles and Pacinian corpuscles. The Meissner's corpuscles have a resonant frequency around 20 Hz and the Pacinian corpuscles have a resonance frequency around 200 Hz. Consequently, the cutaneous sensory system is most sensitive to low audio frequencies and sub sonic vibrations.